Regarding guest_art: what counts as guest art?

Recently, the Idolmaster franchise has started to release character songs with MVs on YouTube, featuring art from several prominent artists. So far, these are the two examples:
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post #5941271

Should these be tagged as guest_art? Do these fall under that umbrella since they're commissioned by the franchise from outside artists? Furthermore, this brings up the question of gacha game art (e.g. character art, craft essences, special art for events, etc.). Does that count as guest_art as well?
Some examples of gacha art not tagged as guest_art:
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post #3893970

Some examples of gacha art tagged as guest_art:
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post #5322798

So, is tagging official gacha art drawn by outside artists as guest_art something worthwhile or will it dilute the tag and distract from more obvious examples of guest art, like anime endcards? (ex. post #5854534)

The idea that "guest art" is just "official art created by a guest artist" seems questionable, especially when it comes to gachas given they largely tend to commission artists to make art for them. This would make guest art and official art overlap in 90% of cases in many of them. In Arknights, to my knowledge, most character art, game CGs, and other artworks/wallpapers they post to Twitter/Weibo/etc are not done by in-house artists, but are instead commission work, meaning basically all of arknights official_art would be tagged guest art. I don't think diluting it that badly is helpful, but I'm also not sure what exactly should be in that tag then.

When I think "guest art" I would more think something like an artbook with a few bonus pieces as the "guest art", but I dunno if that's too narrow.

In Arknights, to my knowledge, most character art, game CGs, and other artworks/wallpapers they post to Twitter/Weibo/etc are not done by in-house artists, but are instead commission work, meaning basically all of arknights official_art would be tagged guest art. I don't think diluting it that badly is helpful, but I'm also not sure what exactly should be in that tag then.

Yeah, as well as ones for Azur Lane. You see some (mainly the ones for loading screens in AL's case) uploaded by the artists on Pixiv so...

My two cents: The Shiny Colors examples are a good example of what guest art should be. These are one-off promotional pieces that are clearly using the artist as a "special guest", and allowing them to create art that is different from the game's house style. The fact that they are being used for music videos makes them a bit more integral to the work than just end cards, but I think you can still clearly draw a line between these and the actual video game (where the same songs appear with no particular art style change).

The wiki already states: "Don't use this tag for images posted in collaborative works where no one artist dominates the artwork, even if one artist officially edits and publishes the work and/or solicits work from other artists.". So if a series follows the footsteps of Kantai Collection and asks artists to draw character designs with no particular house style, then it's not a "special guest" situation, that's just the baseline for how the series looks. I think we should blanket exclude character portraits and profiles from such series.

There are probably also a lot of untagged posts hiding in pool #1338, excluding the ones that aren't officially sanctioned.